Effect of Delayed Lifting After Topping on
PROCEEDINGS—FOURTH GENERAL MEETING 103 Materials and Methods
A field of sugar beets of the variety U.S. 15 growing under favorable conditions near Brawley, Calif., was selected for these studies. The beets were planted on beds with two rows 14 inches apart on each bed. The space between rows of two adjacent beds was 28 inches. The fertility level of' the soil in this field was equivalent to that of the better soils of Imperial Valley. The portion of the field chosen had an exceptionally good stand of uniform beets spaced ap- proximately 12 inches apart in the row. The plan of experimentation involved use of a strip of 26 rows approximately 500 feet long. On J u l y 4 all the sugar beets in the experimental area were topped and the crowns and leaves were raked from the top of the bed into the furrow. Eight of the rows were lifted with a beet lifter and the other 18 rows were left unlifted. The lifting operation severed the roots from the soil and lifted them slightly above their growing position.
Immediately after lifting, 16 samples of 15 beets each were taken at random for analysis from the experimental area. These were divided into two groups of eight 15-beet sanrpies each. There was no signifi- cant difference in sucrose percentage between these two groups. It was, therefore, concluded that eight 15-beet samples constituted an adequate sample. Subsequent sampling was at random for the ex- perimental area concerned, eight. 15-beet samples being taken at each sampling period. Samples were taken immediately and at intervals of 2, 4, 6, 8, and 10 days after topping for the test in which the beets were topped but not lifted, and at intervals of 3, 6, and 9 days in the test in which the beets were topped and lifted.
Chemical Analysis
In these studies harmful nitrogen is considered as the nitrogen not. precipitated by copper hydroxide minus the total ammonia nitro- gen (ammonia plus a m i d ) . The met hods used for determining harmful nitrogen were essentially those developed by European investigators.
These methods are as follows: Three hundred fifty milliliters of dis- tilled water were added to 100 grams of beet pulp and placed in a water bath at 85° C. Fifty milliliters of copper sulphate solution (60 grams of copper sulphate in 1,000 ml. of water) and 50 milliliters of sodium hydroxide solution (12.5 grams of sodium hydroxide in 1,000 ml. of water) were added and thoroughly mixed. The samples were then allowed to digest 15 minutes, with frequent shaking. The sam- ples were cooled to room temperature, the air expelled, made up to volume of 500 ml. and filtered through dry paper pulp. An aliquot of 50 ml. was removed for the determination of the nitrogen not pre- cipitated by the copper hydroxide. Total nitrogen was determined by a standard method which does not include the nitrates. An aliquot of 125 ml. was removed for the determination of ammonia plus amid
104 AMERICAN SOCIETY S U G A R - B E E T TECHNOLOGISTS
nitrogen. The samples were made 1 n o r m a l with sulfuric acid a n d were hydrolized for 2 hours, cooled, then neutralized with sodium hydoroxide. The samples were made alkaline with 40 ml. of an alka- line borate mixture (0.5 normal sodium h y d r o x i d e in 5 percent borax) and the ammonia distilled off at atmospheric pressure.
To eliminate so far as possible e r r o r s due to differences in per- centage d r y matter between fresh and flaccid beets, all samples har- vested after the first day having a higher percentage of d r y m a t t e r than fresh beets were corrected to approximately the percentage d r y m a t t e r of the fresh beets.
Determinations of sucrose percentages followed the procedure used by the Division of S u g a r P l a n t Investigations, U. S. D e p a r t m e n t of A g r i c u l t u r e . Each 15-beet sample was washed a n d drained. E a c h root of the sample was split longitudinally a n d the pieces were passed u n d e r a circular rasp. A fine p u l p was r a s p e d from each half beet section and thrown from the circular r a s p in a series of layers on a metal band. The entire mass of p u l p was taken from the band and thoroughly mixed by an electrically operated mixer. Twenty-six grams of p u l p were taken for determination of sucrose percentage.
Extraction of sucrose was by the cold water digestion method of Krueger, us modified by Sachs a n d Le Docte. Two h u n d r e d grams of pulp) from each of the eight 15-beet samples were placed in a freezing chamber a n d kept frozen until analyzed for nitrogen con- stituents.
For reducing sugars, 10 grams of p u l p were placed in a 100 ml.
Kohlrausch flask and sufficient n e u t r a l lead acetate a d d e d to clear the extract before the volume was made up to mark. The filtered ex- t r a c t was deleaded with sodium oxalate and again filtered. Reducing sugars were determined on an aliquot, usually 50 ml., of the lead-free filtrate by the M u n s o n - W a l k e r method3.
Raffinose was determined by an official method 3 for beet pro- ducts, using hydrochloric acid to invert the sugars before the second polariscope reading.
Experimental Results
Changes in d r y matter, h a r m f u l nitrogen, sucrose, r e d u c i n g sugars, a n d raffinose of beets topped and lifted and t o p p e d but not lifted are presented in table 1. A s u m m a r y of the results is presented in figure 1. A significant increase occurred in percentage of d r y m a t t e r from the first to the ninth d a y of the exposure period in the
3Association of Official Agricultural Chemists 1934 Official and Tentative Method of Analysis, Washington, D. C.
PROCEEDINGS—FOURTH GENERAL MEETING 105
DAY5 EXPOSED
Figure 1.—Changes in chemical constituents of sugar beets when topped and left in place with and without lifting.
106 AMERICAN SOCIETY S U G A R - B E E T TECHNOLOGISTS
beets topped and lifted. In the beets topped but not lifted there was a g r a d u a l a n d significant decrease in percentage of d r y m a t t e r . This decrease suggests that the beets absorbed moisture from the soil after the tops had been removed. In h a r m f u l nitrogen, beets t o p p e d a n d lifted showed a significant increase from the first to the n i n t h day of exposure. In beets topped b u t not lifted the h a r m f u l nitrogen showed a gradual decrease u n t i l the eighth day, a n d then there was a sharp rise on the tenth day t h a t was statistically significant. Sucrose percentage in the lopped and lifted b e d s showed a gradual a n d sig- nificant decrease from the t h i r d to the ninth day. In beets topped but not immedialely lifted, the sucrose fluctuated somewhat but sig- nificant decrease occurred at the t e n t h day. In r e d u c i n g sugars, beets topped a n d lifted showed a significant increase from the t h i r d to the n i n t h day of exposure. As the period in the soil increased, there was a gradual increase in r e d u c i n g s u g a r s in beets topped a n d not immediately lifted, with a s h a r p increase o c c u r r i n g at the t e n t h day of exposure.
Summary and Conclusions
A field test was conducted in the Imperial Valley of California in which comparisons were made of changes which took place in sugar beets topped and left u n d i s t u r b e d with those in which the sugar beets were topped and lifted. This test shows t h a t sugar beets topped in place and left unlifted from 1 to 3 days did not change significantly in dry matter, harmful nitrogen, sucrose, or r e d u c i n g sugars, while beets topped and lifted changed significantly in h a r m f u l nitrogen within a 3-day period after the lifting operation. This test also shows that changes occur more r a p i d l y a n d to a g r e a l e r extent after the root connections with the soil are broken. It would therefore seem that, after lifting, p r o m p t removal from the soil, loading, and h a u l i n g to the receiving station are advisable.
Literature Cited
1. Price, Charles et. al. Sucrose Loss a n d Changes of Nitrogen Con- stituents in S u g a r Beets u n d e r Conditions of Delayed T o p p i n g . J o u r . Amer. Soc. Agron. 3 3 : 901-907. 1941.